Assemblies composed of metallic components are commonly employed in applications requiring corrosion resistance. One such application is in the fuel system of an internal combustion engine, which requires a degree of resistance to various fuels on the inside of the rail body and various other parts of the system which are generally brazed together. Steel tubing and other steel components used in the fuel system, such as fuel rail bodies, cause the oxidation of the gasoline passing through the system unless these components are provided with a corrosion resistent coating on the interior thereof. The oxidation of the gasoline results in the formation of what is known as "sour gasoline".
Furthermore, there has been increased experimentation with alternative fuels, such as methanol. These fuels may cause corrosion of the fuel rail body itself unless the interior of the system is provided with an adequate corrosion resistent coating.
It is well known that nickel and nickel alloys are well adapted for use where corrosion resistance is required. Likewise, methods of applying nickel alloy coatings are well known. One method of commercial nickel phosphorus electroplating is described in U.S. Pat. No. 4,673,468 to Myers et al. An electroless method of applying a nickel alloy coating is described in U.S. Pat. No. 3,069,765 to Simpelaar.
Numerous methods of applying a corrosion resistant coating to the interior of the fuel system assemblies of an internal combustion engine have been attempted. The coatings have heretofore generally been applied after the various components have been joined together using conventional brazing techniques. Thus, the metallic components are bonded together by conventional brazing methods, and then a corrosion resistent coating is deposited on the interior of the assembly. This process, however, has not been completely successful, especially with respect to the coating of the interior of the rail bodies of a fuel system. Disadvantageously, when the coating is deposited after assembly of the components, the layer of corrosion resistent material which results is not completely continuous over the interior of the assembly, allowing oxidation of the fuel at the uncoated sites.